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Biomedical subjects

U Thorgeirsson

Publications and source records attributed to U Thorgeirsson.

9 recordsLinked to original sources
PubMed1995

In vivo induction of liver P-glycoprotein expression by xenobiotics in monkeys.

P-glycoprotein (pgp), the protein product of the multidrug resistance (mdr) gene family, can confer a multidrug resistance (mdr) phenotype to cells in which it is expressed. One member of the pgp family, pgp2, is located on the hepatocyte biliary pole where it may have a role in biliary excretion. Using primates we sought to determine if mdr gene expression and pgp levels were affected by xenobiotics excreted via the bile in man. Five drugs were studied in male and female rhesus monkeys: erythromycin, rifampicin, tamoxifen, diethylstilbesterol (DES), and probenecid. For each xenobiotic, with the exception of DES, an increase in mdr2 mRNA was observed. The results suggest that expression of mdr2 is responsive to xenobiotics, or their metabolites, that require biliary excretion. We speculate that the mdr2 gene may be a member of a class of xenobiotic responsive genes coding for proteins that actively excrete xenobiotics and/or their metabolites into the bile.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Modulation of type-IV collagenase activity and invasive behavior of metastatic human melanoma (A2058) cells in vitro by monoclonal antibodies to type-IV collagenase.

Monoclonal antibodies (MAbs) against human type-IV collagenase were developed and used for studies on enzyme activity and tumor-cell invasion in vitro. Fifteen MAb clones were generated against the enzyme purified form serum-free culture medium of human melanoma cells (A2058). Five clones affecting the activity of type-IV collagenase were selected for further characterization. All the selected clones could be used for a single-step purification of type-IV collagenase using IgG-Sepharose affinity columns. One of the antibodies activated the enzyme when 3H-proline-labelled type-IV collagen was used as substrate. The activation was dependent on the enzyme antibody ratio. Four clones caused more than 30% inhibition of the activity, maximal inhibition being 50%. Interestingly, the same antibody which activated the enzyme also increased the invasion of A2058 cells through a reconstituted basement membrane in an in vitro invasion assay. The 4 inhibitory antibodies decreased the penetration of A2058 cells through the reconstituted basement membrane. The results strongly support previous findings about the importance of type-IV collagenase in tumor-cell invasion.

Antibodies, Monoclonal↗
PubMed1988

Biochemical mechanisms of tumor invasion and metastases.

Cancer invasion and metastases is a complex multistep process. In order for a tumor cell to successfully traverse all the steps of this process and initiate a metastatic colony, it must express the right combination of gene products. Such gene products may include proteins which regulate cell interaction with the basement membrane and cell motility. Tumor cells attach to the basement membrane glycoprotein laminin via the cell surface laminin receptor. The human laminin receptor was purified and molecularly cloned. The level of laminin receptor mRNA is a variety of human carcinoma cells correlated with the number of laminin receptors on the cell surface of these cells. Following attachment to the basement membrane, the tumor cell next secretes proteases which may degrade type IV collagen. A genetic linkage between type IV collagenase secretion and metastases was studied using our new genetic system for inducing metastases employing the ras oncogene. Following attachment and local proteolysis, the third step of invasion is tumor cell motility. We have isolated a tumor cell autocrine motility factor (AMF). This factor is secreted by the tumor cells and binds to a cell surface receptor resulting in a profound (greater than 100x) stimulation of cell locomotion. AMF may play a major role in the autonomous invasive behavior of tumor cells.

Animals↗
PubMed1988

Biochemical mechanisms of tumor invasion and metastases.

Cancer invasion and metastases is a complex multistep process. In order for a tumor cell to successfully traverse all the steps of this process and initiate a metastatic colony, it must express the right combination of gene products. Such gene products may include proteins which regulate cell interaction with the basement membrane and cell motility. Tumor cells attach to the basement membrane glycoprotein laminin via the cell surface laminin receptor. The human laminin receptor was purified and molecularly cloned. The level of laminin receptor mRNA is a variety of human carcinoma cells correlated with the number of laminin receptors on the cell surface of these cells. Following attachment to the basement membrane, the tumor cell next secretes proteases which may degrade type IV collagen. A genetic linkage between type IV collagenase secretion and metastases was studied using our new genetic system for inducing metastases employing the ras oncogene. Following attachment and local proteolysis, the third step of invasion is tumor cell motility. We have isolated a tumor cell autocrine motility factor (AMF). This factor is secreted by the tumor cells and binds to a cell surface receptor resulting in a profound (greater than 100x) stimulation of cell locomotion. AMF may play a major role in the autonomous invasive behavior of tumor cells.

Animals↗
PubMed1987

Biochemical mechanisms of tumor invasion and metastasis.

Cancer invasion and metastases is a complex multi-step process. In order for a tumor cell to successfully traverse all the steps of this process and initiate a metastatic colony, it must express the right combination of gene products. Such gene products may include proteins which regulate cell interaction with the basement membrane and cell motility. Tumor cells attach to the basement membrane glycoprotein laminin via the cell surface laminin receptor. The human laminin receptor was purified and molecularly cloned. The level of laminin receptor mRNA in a variety of human carcinoma cells correlated with the number of laminin receptors on the surface of these cells. Following attachment to the basement membrane, the tumor cell next secretes proteases which may degrade type IV collagen. A genetic linkage between type IV collagenase secretion and metastases was collagen. A genetic linkage between type IV collagenase secretion and metastases was studied using our new genetic system for inducing metastases by employing the ras oncogene. Following attachment and local proteolysis, the third step of invasion is tumor cell motility. We have isolated a tumor cell autocrine motility factor (AMF). This factor is secreted by the tumor cells and binds to a cell surface receptor, resulting in a profound (greater than 100 x) stimulation of cell locomotion. AMF may play a major role in the autonomous invasive behavior of tumor cells.

Animals↗
PubMed1986

Laminin promotes rabbit neutrophil motility and attachment.

Polymorphonuclear neutrophils (PMN) traverse basement membrane to reach sites of infection. We have studied the role of laminin, a specific basement membrane component, in this process using three assay systems. In the Boyden chamber, laminin was found to stimulate chemotaxis of neutrophils while fibronectin did not. Co-incubation of cells with antibody to laminin blocked this chemotaxis, while antibody to fibronectin was without effect. In the human amnion system, neutrophils were shown to penetrate through the tissue when the peptide chemoattractant f-Met-Leu-Phe was placed on the opposing side. Antibody to laminin, but not to fibronectin, blocked this penetration. In an attachment assay system, laminin, but not fibronectin, was found to increase dispase-treated neutrophil attachment to type IV (basement membrane) collagen-coated plastic and to a plastic substrate itself. Electrophoretic analysis of PMN extract indicated the presence of laminin, and indirect immunofluorescence suggested that laminin is localized on the surface of the neutrophils. These data suggest that PMN can bind laminin on their cell surfaces, use laminin to attach to basement (type IV) membrane collagen, and migrate toward a gradient of laminin. These properties may be important for the passage of neutrophils from the circulation to sites of infection.

Amnion↗
PubMed1981

The parathyroid glands in familial hypocalciuric hypercalcemia.

We analyzed, by light microscopy, specimens obtained at parathyroid surgery from 18 members of eight kindreds with familial hypocalciuric hypercalcemia. For comparison, similar analyses were performed with normal parathyroid glands (surgical or postmortem specimens) and with glands from patients with typical primary parathyroid hyperplasia. The average parathyroid parenchymal area in familial hypocalciuric hypercalcemia was 300 per cent of that in normal subjects (0.049 versus 0.15 sq. cm., p less than 0.0005) but significantly less than that in typical primary parathyroid hyperplasia. Thirteen of the 18 subjects with familial hypocalciuric hypercalcemia had one or more enlarged glands. Enlarged parenchymal areas were noted at all ages in familial hypocalciuric hypercalcemia, but there was a spectrum of histologic findings among the glands in each case, within most families, and between families. Mild parathyroid hyperplasia was a feature in most patients with familial hypocalciuric hypercalcemia who had undergone neck surgery. Simple quantitative analyses were useful in identifying parathyroid hyperplasia in the group with familial hypocalciuric hypercalcemia.

Adolescent↗
PubMed1981

Polymorphonuclear leukocyte migration through human amnion membrane.

A new in vitro model has been developed for studying migration of human polymorphonuclear leukocytes (PMN) through living native cellular and matrix barriers. Human amnion membrane consists of a single layer of epithelium bound to a continuous basement membrane interfacing an avascular collagenous stroma. Living amnion was placed in plastic chambers with separate compartments on each side of the membrane. PMN were introduced on the epithelial side of the amnion, and a Millipore filter (Millipore Corp., Bedford, Mass.) was placed against the stromal side. In response to N-formylmethionyl-leucyl- phenylanlanine (FMLP) chemoattractant, PMN penetrated the full thickness of the amnion and were collected and counted on the filter. The rate of PMN traversal of the amnion was dependent on the concentration of FMLP (optimal at 10(-8)M) as well as the slope of the FMLP gradient across the amnion. The route of PMN migration was studied by transmission electron microscopy. PMN first attached to the epithelial surface, then infiltrated between intercellular junctions. PMN migrated around or through tight junction and hemidesmosome attachments. The PMN then penetrated the basement membrane and migrated through the dense collagenous stroma. The present amnion migration system has characteristics of the in vivo inflammatory state not described in any previous method for monitoring PMN migration in vitro. Prior methods have not used native epithelium, whole basement membrane, or collagenous stroma. PMN penetration of these barriers occurs in the normal inflammatory response and probably involves biochemical mechanisms not required for simple migration through the pores of an artificial filter. The amnion system can be useful for future biochemical and morphological studies of PMN penetration of these barriers and possible repair processes that may follow.

Amnion↗